Background:

The tribe Tigridieae (Iridaceae) is a monophyletic group restricted to America. It includes bulbous perennial plants with plicate and isobilateral leaves. The inflorescence is a rhipidium and the floral structures are fugacious, very variable in shape, color and size. Tigridieae is taxonomically and morphologically complex. Its generic limits are unresolved and the vegetative uniformity of the tribe complicates species identification. Species are recognized by the position, shape and color of the tepals, stamens and stigma, characters that are difficult to observe in many herbarium specimens.

Studied species:

Sixty-seven species of the tribe Tigridieae.

Study site and years of study:

North America (Canada, United States of America and Mexico). The study was conducted from 2009 to 2015.

Methods:

Twenty-three herbaria, floristic studies and monographs were reviewed and specimens were collected in the field. Fresh dissections were performed in order to preserve the flowers and an analysis was conducted of the floral variation and distribution of the species of Tigridieae.

Results:

Keys for the identification of genera and species are presented. Photographs of the species and floral structures are included for their recognition. In addition, a method is described for dissecting and preserving flowers as herbarium specimens. Finally, geographic distribution data are presented.

Conclusions:

In North America, 67 species within14 genera of Tigridieae are known, of which 54 are endemic. Tigridieae exhibits wide floral diversity influenced by its pollinators and geographic isolation. This key for the Tigridieae of North America along with the photographs illustrating floral diversity will facilitate identification of species in the field.